An instrument of this description is known from U.S. Pat. No. 3,638,644 to F. G. Reick. The laryngoscope particularly disclosed in that patent utilizes a solid light guide, in the form of a curved strip of polyacrylate (Lucite or Plexiglas) terminating in a reduced front end at the tip of the applicator and in a broader rear end which in a working position is closely spaced from an aperture at the top of the handle overlying a light bulb. The latter is part of a lamp closely surrounded by a metallic sleeve in direct contact with the metallic shell of the handle which in turn is conductively connected, through a biasing spring at the bottom of that handle, with the negative pole of a battery stack whose positive pole is normally held separated, by means of another spring, from a centrally disposed terminal of the light bulb. When the applicator is swung into its working position, via a pivotal junction linking it with the handle, a pair of feet of that applicator cammingly engage the metallic sleeve in order to repress the lamp against the force of the last-mentioned spring so as to let its central terminal make contact with the positive battery pole whereby the bulb is energized to illuminate the proximal end of the acrylic strip. An abutment rising from the top of the head carries detent balls coacting with recesses on the feet bracketing same in order to index the applicator in its working position.
As noted in that patent, Lucite is a brittle and fragile material wherefore the light-guiding strip has to be supported on the applicator by a depressor blade made from a tough resin, namely polycarbonate. The strip is flanked on one side by a reinforcing rib but is otherwise exposed, except at its rear end where it is shielded by a glare cover.
The described camming mechanism for closing the lamp circuit has the drawback that the light bulb may be accidentally energized, with consequent discharge of the associated batteries, even when the applicator or speculum is in its inoperative or idle position. This could happen, for example, when the bulb is inadvertently repressed by hand or when its sleeve jams in the repressed state after a temporary swing of the applicator into its working position. In case of a burnout, extraction of the bulb from its socket for the purpose of replacement requires the use of a special tool.